Chapter 2: Prenatal Development, Pregnancy, and Birth.

Chapter 2:

Prenatal Development, Pregnancy, and Birth

FERTILIZATION:THE REPRODUCTIVE SYSTEMS

Female Reproductive Structures

• Uterus• Endometrium

• Cervix (neck of uterus)

• Fallopian tubes

• Ovaries• Ova reside here

• Ova contain mother’s genetic material

REPRODUCTIVE SYSTEMS

Male Reproductive Structures

• Testes (continually manufacture sperm)

• Penis

PROCESS OF FERTILIZATION: UNION OF SPERM AND EGG

• Ovulation occurs: • ovum expelled from ovary • suctioned into fallopian tube

• Millions of sperm travel up fallopian tube to ovum

• Fertilization• One sperm penetrates the ovum.• Nuclei (genetic material) of the male and

female cells combine.

• Chromosome▫ Located in the nucleus of every cell, a

threadlike strand of DNA, which carries the genes that transmit genetic information

• DNA (deoxyribonucleic acid)▫Material that makes up genes, which

bear our hereditary characteristics• Gene▫ A segment of DNA that contains a

chemical blueprint for manufacturing a particular protein

GENETICS: CHROMOSOMES, DNA, GENES

• 23 chromosome pairs contain DNA (genetic material)▫ 23 single strands each from mother

and father▫ Sex chromosome = 1 chromosome

pair (XX female, XY male)

GENETICS: CHROMOSOMES, DNA, GENES

KARYOTYPE

STAGES OF PRENATAL DEVELOPMENT• Germinal

• First 14 days, from fertilization to implantation

• Period of Zygote• Embryonic

• Week 3 to 8

• Period of Embryo• Fetal

• Week 9 to Birth

• Period of Fetus

• Zygote (fertilized ovum)

• In the first 36 hours, zygote divides once

• Divides again every 12-15 hours • Travels down fallopian tube for 3 days• Once in the uterus, differentiates into

layers— zygote is identified as a blastocyst and has roughly 100 cells

• Blastocyst implants into the upper part of the uterus

• Blood vessels proliferate to form the placenta

GERMINAL STAGE, FIRST TWO WEEKS: FROM ZYGOTE TO BLASTOCYST

BLASTOCYST

EMBRYONIC STAGE: WEEKS 3 TO 8

• Fast paced; all major organs constructed• 3rd week, circulatory system forms and heart beats• 20 to 24 days neural tube forms—differentiates into brain and spinal

cord• Day 26, arm buds form• Day 27, leg buds appear• Feet, elbows, wrists, and fingers begin to appear.• By week 8, the embryo is 1.5 inches long.• The internal organs are in place and embryo begins to look human.

PRINCIPLES OF PRENATAL DEVELOPMENT• Proximodistal

• Growth from middle to outside

• Cephalocaudal

• Growth from head to tail (feet)

• Mass to Specific

• Large structures appear before finer details.

• Large movements appear before finer movements.

WEEKS 3, 4, AND 9 OF EMBRYONIC STAGE• Note proximodistal and cephalocaudal trends

Week 3 Week 4 Week 9

FETAL STAGE: WEEK 9 TO BIRTH

• Baby grows dramatically:• Body structures are refined.

• Building blocks of the brain are fully assembled.

• Neurons ascend to the top of the neural tube, reach their staging area, and begin to differentiate.

Climbing Neurons

FETAL STAGE

• Age of viability is 22 weeks (earliest date for possibility of survival).• Vital that baby’s lungs are mature enough to breathe in oxygen and

to expel carbon dioxide.

• By the 25th week, viability is above 50% if acute care is available.

• Birth weight is important to health of baby.• Baby needs as much time in the womb as possible.

• During the last 2 months, fetus gains almost 5 pounds.

POISED TO BE BORN!

• Fetus positioned in the womb late in pregnancy.

• Notice the placenta, amniotic sac, and umbilical cord.

PREGNANCY

• Gestation Period: 267-277 days▫Divided into trimesters (about 3 months each)▫ Important! Each woman may vary in her experience (physical and

emotional) of pregnancy.• First Trimester▫Following implantation of blastocyst into uterus, flood of hormones

may produce fainting, headaches, fatigue, tender breasts, and morning sickness. Progesterone; human chorionic gonadotropin (HCG)

▫Miscarriages (spontaneous abortions) more prevalent at this time: Roughly 1 in 10 pregnancies ends in miscarriage. Miscarriage rate increases to 1 in 5 for women in their late thirties.

PREGNANCY: SECOND TRIMESTER• Physically may feel much better

• By week 14, uterus grows (maternity clothes!)

• Quickening occurs (first indication of movement of the fetus)

• Feelings of attachment may begin

• A strong sense of attachment during pregnancy predicts positive bonding after birth.

PREGNANCY: THIRD TRIMESTER• Physical Symptoms and Emotional States

• Leg cramps, backaches, numbness in lower limbs, heartburn, insomnia

• Irregular uterine contractions as baby sinks into the birth canal

• Anxious anticipation may begin as the focus shifts to the birth.

PREGNANCY IS NOT A SOLO ACT Forces that may contribute the experience of distress during pregnancy

Economic concerns; low SES places women at risk of feeling demoralized and depressed possible lack of access to prenatal care, proper foods, and often,

social support Positive forces

Presence of a loving partner may predict a happy pregnancy. The perception of being cared about and loved; a sense of connectedness

Husbands also may experience strong emotions. May feel concerned about this life change Social support necessary

THREATS TO THE DEVELOPING BABY: BIRTH DEFECTS CATEGORY 1: TERATOGENS

• Teratogens: substances that may cross the placenta to harm the developing embryo or fetus

• Teratogens do most damage during sensitive periods.

• Four Principles▫ Most likely to cause structural damage during embryonic period▫ Can affect developing brain throughout pregnancy

2nd and 3rd trimester: risk of developmental disorders▫ Operate in a dose-response fashion (threshold level)▫ Exert damage unpredictably, depending on fetal and maternal

vulnerabilities• Teratogens may also exert influence long after exposure.

BIRTH!

• Stage 1: Dilation and Effacement

• Stage 2: Birth

• Stage 3: Expulsion of the Placenta

• Threats during birth include: • baby in breech position

• cervix not fully dilating

• difficult position of umbilical cord

BIRTH OPTIONS• Birth options and providers:

• Natural childbirth• Deliver without medication with the help of midwife or doula.

• Lamaze (pain management)

• Bradley (natural, non-medicated childbirth)

• Sometimes, medical intervention is needed.

• Cesarean Section• Procedure common in some countries

• Used in the United States if complications occur

MEDICAL INTERVENTIONS• Episiotomy

• Epidural

• Electronic Fetal Monitor

• Cesarean Section (C-Section)

• Remove fetus manually by making incision into abdominal wall and uterus

• Used when complications occur

THE NEWBORN• Apgar Scale: first test immediately after birth

• Rated 0 to 2 for each category at 1 minute and 5 minutes after birth• Color• Muscle Tone• Respiration• Heart Rate• Reflex Response• Score over 7, healthy• Under 7, must be monitored or resuscitated and may go to NICU

(neonatal intensive care unit)

THREATS TO DEVELOPMENT

• Low birth weight (LBW)

• Body weight of less than 5½ lbs.

• Arrived too early or did not grow in womb

• Very low birth weight

• Body weight of less than 3¼ lbs.

• Often very premature and rushed to NICU

INFANT MORTALITY: DEATH DURING FIRST YEAR OF LIFE

• Varying mortality rates among countries

• Notice difference between developing and developed countries

Deaths of children under 1 year of age in 2011